The present invention relates to a process for continuous production of copolyamides based on a lactam (I), a diamine (II) and a dicarboxylic acid (III), which comprises
reacting a mixture (IV) comprising a diamine (II), a dicarboxylic acid (III) and water in a first reaction zone at a pressure in the range from 1.3*105 to 2.5*105 Pa in the entry zone of the reaction zone and at a temperature above the melting point of polymer (V) to a conversion, based on the molar amounts of diamine (II) and dicarboxylic acid (III), of at least 80% to form a polymer (V),
reacting a mixture (VI) comprising lactam (I) and water in a second reaction zone at a pressure in the range from 5*105 to 40*105 Pa in the entry zone of the reaction zone and at a temperature above the melting point of polymer (VII) to a conversion, based on the molar amount of lactam (I), of at least 80% to form a polymer (VII),
then reacting polymer (V) and polymer (VII) with each other in a third reaction zone at a pressure in the range from 1*105 to 1.5*105 Pa in the entry zone of the reaction zone at temperatures above the melting point of polymer (VIII) to form a polymer (VIII), said polymer (VIII) having a 95xc2x0 C. water extractables content, based on lactam (I), diamine (II) and dicarboxylic acid (III), of not more than 10% by weight, and
then extracting the polymer (VIII) with water to obtain the copolyamide.
The present invention further relates to copolyamides obtainable by this process, to their use for producing fibers, sheetlike structures and shaped articles, and to fibers, sheetlike structures and shaped articles based on the copolyamides.
Processes for continuous production of copolyamides from lactams, such as caprolactam, and equimolar amounts of diamines and dicarboxylic acids, such as hexamethylene adipate (xe2x80x9c66 saltxe2x80x9d), are common knowledge.
DD 110 507 describes such a process where caprolactam, 66 salt and water are fed to the top of a vertical column reactor (VK tube) and polymerized in the tube at elevated temperature and elevated pressure by passing the reaction material downwardly through the tube, and at the same time removing the corresponding copolyamide at the bottom end of the tube one disadvantage with this process is that vapors escape at the top of the VR tube; this makes it difficult to obtain a consistent high product quality, since the vapors also carry out diamine and, moreover, precise temperature control in the top region of the VK tube is made difficult. In addition, only a small amount of heat can be introduced into the reaction system via the top of the VK tube, so that only small amounts of diamine and dicarboxylic acid become incorporated in the copolyamide in this process. Another disadvantage of the process is that long residence times of about 19 hours are needed for the reaction mixture in the VK tube in order to obtain economical conversions and copolyamides having marketable product properties.
EP-A-0 098 412 discloses a process for the production of copolyamides. In this process, to avoid the reaction material solidifying as a result of the evaporation of the water of reaction, an aqueous 66 salt solution is continuously added at atmospheric pressure to an appropriate prepolymer melt, the temperature of which should never be less than a certain minimum value, and the water is distilled off at the same time. The continuously removed melt is further condensed at atmospheric pressure in a conventional manner. This process likewise has the disadvantage of the maintenance of a constant temperature in the face of the evaporation of the water of reaction. In addition, the precondensation gives rise to losses of diamine, so that a consistent high product quality is difficult to achieve in this process too.
EP-A-0 393 546 discloses a process wherein an aqueous solution of equimolar amounts of a diamine and of a dicarboxylic acid is passed through a tubular reactor at slightly elevated pressure and with concurrent evaporation of water to form a vapor phase and a prepolymer. The prepolymer melt is subsequently mixed with molten caprolactam and passed downwardly through a VK tube to form a copolyamide. The vapors formed at the entrance to the VK tube are separated in a distillation column by removing water vapor via the top of the column and recycling an aqueous diamine solution into the polymerization. One disadvantage with this process is the low flexibility with regard to the production of copolyamides of different morphologies, ie. the distribution of units based on caprolactam and of units based on diamine and dicarboxylic acid within the copolyamide, for the same gross composition. In addition, the process, which requir s VK tube residence times of 8 to 14 hours, provides only a low space-time yield.